The long term goals of the proposed studies are to characterize the functions of the fragments of C3 and to define the structural basis for these functions. Initial efforts are thus directed toward the complete structural characterization of all C3 fragments generated in vitro and in vivo. The amino and carboxy terminal sequences of each fragment and their constituent peptides will be determined. The structure of the fragments generated by complement activation in vitro will be compared with the structure of fragments isolated from patients with complement activation in vivo. The structure of two peptides which appear to be present in much greater quantities with in vivo complement activation than in vitro will also be determined. The C3 fragment responsible for the induction of leukocytosis will be characterized. This will be done using a synthetic peptide which corresponds to a 9 residue C-terminal segment of the C3c Mr 27000 peptide, with C3dg, with C3c, and with peptides derived from C3c by digestion with proteases. The C3 fragments involved in the inhibition of T-lymphocyte mitogenesis and the cells (T lymphocyte or macrophage) involved in this inhibition will be defined. The potential efects of C3 fragments on the synthesis of C3 by human monocytes in vitro will be determined, as will the effects of serum from individuals with depressed C3 synthesis. The C3 fragments deposited in kidneys in various glomerular diseases will be identified initially by immunofluorescence studies using monoclonal antibodies which react with different C3 fragments. Binding studies using radiolabelled antibody will also be performed to quantitate the amounts of different fragments present in kidneys in different diseases. Other experiments will be directed toward demonstration of the structural and functional integrity of the deposited fragments. Lastly, the complete amino acid sequence of conglutinin, a protein which interacts with C3, will be determined. Its binding site for iC3b will be characterized, as will its binding to fibronectin. Conglutinin cDNA clones will be isolated from bovine cDNA libraries. These cDNA clones will subsequently be used to identify a putative human conglutinin gene.